Mining machine drum cutter extension means

ABSTRACT

A mining and loading apparatus and more particularly a continuous-mining apparatus having improved drum cutter extension means for dislodging mineral from a solid mine vein. This drum cutter incorporates a double passageway head shaft for activating hydraulic cylinders to extend and retract extensible drum portions of the drum cutter.

United States Patent Inventor Glenn A. Daily RD. 1, Utica, Pa. 16362Appl. No. 72,239 7 Filed Sept. 14, 1970 Patented Nov. 2, 1971Continuation of application Ser. No.

7 86,648 Dec. 24, 1968, now abandoned.

MINING MACHINE DRUM CUTTER EXTENSION MEANS 13 Claims, 5 Drawing Figs.

[1.8. CI 299/80, 299/67, 299/87 Int. Cl ..E21c 27/24, E2lc 35/20 Fieldof Search 299/64, 67, 75, 80

[56] References Cited UNITED STATES PATENTS 3,305,273 2/1967 Kilbourne299/80 X FOREIGN PATENTS 889,803 2/1962 Great Britain 299/80 182,6418/1966 U.S.S.R........ 299/80 Primary Examiner-Ernest R. PurserAttorney-E. Wallace Breisch ABSTRACT: A mining and loading apparatus andmore particularly a continuous-mining apparatus having improved drumcutter extension means for dislodging mineral from a solid mine vein.This drum cutter incorporates a double passageway head shaft foractivating hydraulic cylinders to extend and retract extensible drumportions ofthe drum cutter.

PATENTEDunv 2 I97l I SHEET 10F 3 IN VEN TOR 4. DAILY PATENTEUun v 2 l9?!SHEEI 2 UF 3 IN VENTOR.

GLENN A. DAILY PAIENTEMnv 2 ran SHEET 3 or 3 MINING MACHINE DRUM CUTTEREXTENSION MEANS This application is a continuation of application, Ser.No. 786,648, filed Dec. 24, 1968 and now abandoned.

In a continuous-mining apparatus of the type employed in this invention,a disintegrating head mechanism is used to dislodge mineral from a minevein and is operable to provide mine passageway or room into which theapparatus advances and mining progresses. The disintegrating headmechanism is pivotably mounted on a mobile base to swing in a verticalplane between the mine roof and floor and includes a rotary drum-cuttinghead assembly arranged on a horizontal transverse axis and having teethor bits which tear away and dislodge the mineral. The apparatus alsoincludes a conventional loading head for gathering the loose mineral onthe mine floor and moving it rearwardly and inwardly toward the forwardreceiving portion of the conveying means of the apparatus. The rotarydrum-cutting head assembly has end portions thereof which can beselectively extended or retracted to, respectively, dislodge mineralfrom the ribs and corners of a mine passageway and reduce the effectivelength of the cutting head assembly to provide clearance at the sides ofthe assembly.

The present invention contemplates improvements over such known types ofmining apparatus, for example, an improved structure and hydrauliccircuit for extending and retracting the end portions of the rotarydrum-cutting head assembly.

These and other objects and advantages of this invention will becomemore readily apparent from the following description and drawings inwhich:

FIG. I is a perspective view of a mining machine embodying theprinciples of this invention;

FIG. 2 is an enlarged view, partly in section, taken on line 2-2 of FIG.1 and showing a main gear casing and a portion of the cutterheadassembly embodying the principles of this invention;

FIG. 3 is an enlarged view, partly in section of a cutterhead assemblyembodying the principles of this invention;

FIG. 4 is an enlarged detail view of hydraulic pressure fluid supplypassageways and sealing means of this invention; and

FIG. 5 is a schematic representation of the hydraulic circuit forextending and retracting end portions of the rotary drum cutting headassembly.

A continuous mining machine, generally designated at 10, with which anoutboard oil seal and oil supply means of this invention is associated,may assume various forms but for illustrative purposes, herein comprisesa crawler base 14 carrying a frame I6 on which a forwardly extendingmining boom 18 is pivotably mounted at the forward end of frame l6toswing up and down between a mine roof and a mine floor. A cutting headassembly 24 extends transversely of boom 18 and is rotatably securedthereto at the forward end thereof. Pivotably mounted at the forward endof frame 16 and extending forwardly therefrom beneath the boom 18 is aconventional loading head 26 having oscillatory gathering arms 28 forengaging mined mineral and moving such mineral rearwardly and inwardlytoward a well-known conveying means 30 of the mining machine 10.Conventional fluid jacks (not shown) serve to swing the boom 18 in avertical plane about the pivot axis thereof and tilt the loading head 26about the horizontal axis thereof. The fluid jacks have one end thereofsecured to the forward end of frame l6 and have the other ends thereofsecured to respective rearward ends of boom 18 and loading heads 26.

The cutting head assembly 24 is driven in any suitable manner frommotors 36, which are suitably rigidly secured by brackets 38 to boom 18.Such a driving arrangement is shown and illustrated in U.S. Pat.application, Ser. No. 786,650, filed Dec. 24, I968, assigned to the sameassignee as is this invention.

The drive from motors 36 rotatably drives a cutting head assembly driveshaft 70. Head drive shaft 70 extends transversely of the longitudinalaxis of mining machine and is captively and rotatably supported bytubular gear casing extensions 72 which extend outwardly (i.e.transversely from the centerline of machine 10) from a forward portion74 of a main gear casing 56. Casing 56 is contained within a forwardarea of boom 18 and is securely fastened to the inner sides thereof inany suitable manner.

As hereinafter described in detail head drive shaft 70 rotatably drives:an endless circulating belt type continuous hinge cutter chain 76 whichhas a width thereof approximately equal to a transverse measurement ofcasing portion 7 4 taken at the forward end thereof; hollow cylindricalrotary drum cutting heads 78 which extend outwardly from respectivesides of portion 74; and hollow cylindrical rotary drum cutting headextension 80 which are slidably partially received within respectiveheads 78 and are selectively hydraulically extendable outwardlytherefrom.

At the longitudinal centerline of machine 10 a cutter chain drivesprocket 82 is in splined engagement with shaft 70. Drive sprocket 82has a plurality of teeth 84 around the outer periphery thereof whichdrivably engage the cutter chain 76. A suitable rear idler sprocket 86which is rotatable on a shaft 88 and extends transversely of the forwardboom area provides well known tensioning and motion reversing means forthe cutter chain 76 to form a continuous orbital path therefor.

Spacer sleeves 90 are positioned along shaft 70 intermediate sprocket 82and adjacent gears 68 so as to maintain a spaced relationship betweensprocket 82 and gears 68. On the outer sides of gears 68 (outer beingaway from sprocket 82 along the centerline of shaft 70) spacer sleeves92 are positioned along shaft 70 to provide a spaced relationshipbetween gears 68 and roller bearings 94 which additionally surroundshaft 70. Roller bearings 94 provide a rotational relationship betweenthe main gear casing 56 and shaft 70 inwardly adjacent the outer ends ofeasing extension portions 72. A spacer sleeve 96 is positioned alongshaft 70 outwardly adjacent the bearings 94. The outer diameter ofspacer sleeve 96 is less than the outer diameter of bearing 94. Annulardrive shaft keepers 98, which are rigidly secured to the outer ends ofcasing extension portions 72 and project radially inwardly from theinner periphery thereof, have the inner surfaces thereof in rotatablecontact with the outer surface of spacer sleeves 96.

Outwardly adjacent to spacer sleeves 96 and keepers 98, internallysplined rotary drum cutting head driving sleeves I00 are in splinedengagement with shaft 70. Sleeves 100 are rigidly secured to the rotarydrum cutting heads 78 intermediate the axial ends thereof and projectradially inwardly from the inner periphery thereof. With such sleeves100 the rotary drum cutting heads 78 are rotatably driven from shaft 70at a rate thereof equal to the rate of cutter chain drive sprocket 82and cutter chain 76. The inner end of cutting heads 78 (inner end beingthat end closest to the longitudinal centerline of machine 10) arerotatably supported by roller bearings 102. Bearings 102 are fixedlysecured about the outer periphery of casing extension portions 72adjacent the inner ends thereof.

Outwardly adjacent to sleeves 100, lock nuts 104 are threadably receivedon shaft 70. When lock nuts I04 are positioned around shaft 70 andtightened into bearing against sleeves 100 at the outer surface thereof:engaging sleeves I00; spacer sleeves 90, 92 and 96, roller bearing 94;and drive sprocket 82 are releasably secured with respect to shaft 70thereby preventing any motion thereof in the axial direction. Transversemovement of shaft 70 with respect to machine 10 is prevented by locknuts I04 transferring thrust from shaft 70 through the sleeves I00 andthe remainder of the cutter heads 78 to the bearings 102.

Each rotary drum cutting head 78 has a radially outwardly extendingflange 106 at the inner ends thereof and a reduced diameter portionthereof forms a chain end supporting seat I08 which extends axially fromflange 106 toward the centerline of machine 10. Further description ofseats I08 and the purpose therefor is shown and illustrated in thehereinbefore mentioned U.S. Pat. application Ser. No. 786,650.

The hollow cylindrical rotary drum cutting head extensions 80 aredimensioned to have an inner portion thereof slidably received within anouter portion of respective cutting heads 78 (inner and outer beingrespectively, toward and away from the centerline of machine lntemallysplined rotary drum cutting head extension sleeves 112 project radiallyinwardly from the inner periphery of head extensions 80 and are locatedoutwardly adjacent the inner ends thereof. Sleeves 112 have the radiallyinnermost surfaces thereof in splined engagement with shaft 70 such thathead extensions 80 are rotatably driven from shafl 70 at a rate thereofequal to the rate of rotation of cutting heads 78. Rotary drum cuttinghead extension keeper sleeves 114 project radially inwardly from theinner periphery of head extensions 80 and are located intermediate theaxial ends thereof. Sleeves 114 have the radially innerrnost surfacesthereof in sliding relationship with the outer periphery ofshaft 70.

Shaft 70 is splined along the outer surfaces thereof from a pointintermediate the axial ends thereof inwardly to the lock nuts 104. Anend cap 116 is secured to the outer end of shaft 70 and extends radiallyoutwardly therefrom. End cap 116 limits the axial movement of headextensions 80 with respect to cutter heads 78 to that distance from theoutermost splined area of shaft 70 outwardly to the end cap 116, forwhen the head extensions 80 extend outwardly such a distance the keepersleeve 114 contacts end cap 116 thereby preventing any further outwardmovement.

Well-known screw-type continuous conveyor scrolls 118 are secured to theouter periphery of rotary drum cutting heads 78 and to well known scrollsupporting sheaths 115 which are secured to outer end portions of therotary drum cutting head extensions 80. Such sheaths 115 allow theextension and retraction of head extensions 80 while still maintaining asubstantially continuous conveying scroll 118 with respect to the scroll118 on heads 78. Scrolls 118 and the cutting chain 76 have a pluralityof suitable bit holders 120 secured adjacent the outer peripheral edgesthereof in a suitable spaced orientation to one another. A cutter bit122 is inserted in each bit holder 120. The scrolls 118 are suitablyarranged to convey a portion of mineral mined by bits 122 inwardly fromsuch bit locations toward the cutting chain 76. End cutter caps 124 aresuitably secured to the outer ends of head extensions 80. But holder 120and cutter bits 122 are secured to caps 124 in a suitable spacedorientation to one another.

An elongated hydraulic fluid conducting tube 128 which has an outerdiameter thereof less than the inside diameter of shaft 70 is mountedwithin shaft 70 in spaced relationship with the inner diameter thereof.As shown the axial ends of tube 128 are symmetrical with respect to thecenterline of machine 10 and in approximate radial alignment with thelock nuts 104 which are positioned around the outer periphery of shaft70 as hereinbefore described. Pilot operated check valves 130 arereceived within respective end portions of shaft 70 and have the inletconnections thereof secured to the axial ends of tube 128 and the outletconnections thereof secured to the head ends of hydraulically extensiblecylinder assemblies 132 which are additionally partially received withinshaft 70. The outer periphery of valves 130 and assemblies 132 is lessthan and spaced from the inner periphery of shaft 70.

Assembly 132 can be of any suitably construction and as shown comprises:a hydraulic cylinder 134 which has the outer ends thereof(outer beingdefined as away from the centerline of machine 10 along the axialcenterline of shaft 70) sealingly secured to the end cap of shaft 70; apiston head 136 which is reciprocably received within cylinder 134; anda piston rod 138 which has the inner end thereof firmly secured topiston head 136 and the outer end thereof secured to the end cutter cap124 at the inner surface thereof.

With such a construction of assembly 132 as hereinabove described, toextend the rotary drum cutting head extensions 80 from an unextendedposition thereof hydraulic pressure fluid is initially supplied asdescribed hereinafter to tube 128.

The pressure fluid continues flowing in tube 128 until such time that asufficient pressure develops therein to cause check valves to open. Thepressure fluid then flows through valves 130 into cylinders 134 therebyurging piston heads 136 forwardly from an unextended position thereof.Because the piston heads 136 are directly connected to respectivecutting heads 78 by means of the piston rod 138, such a forward move topiston heads 136 causes the cutting heads 78 to extend outwardly fromthe unextended positions thereof. Any hydraulic fluid in the portion ofcylinders 134 outward of the piston head 136 is expelled from cylinders134 by means ofa plurality of ports located at the outer end ofcylinders 134. Such fluid is expelled through ports 140 into an annularpassageway 142 which is defined by the annular space between the outerperipheries of cylinders 134, check valves 130 and the fluid tube 128and the inner periphery of shaft 70. Fluid flowing through passageway142 is expelled therefrom through casing retraction passageways ashereinafter described.

When the head extensions 78 are extended to a desired position, thepressure fluid supply to tube 128 is discontinued thereby resulting invalves 130 closing and, because the fluid in cylinders 134 intermediatevalves 130 and piston head 136 is incompressible, the head extensions 78are locked into position with respect to any inward movement thereof.

To retract the rotary drum cutting head extension 78 from an extendedposition thereof hydraulic fluid is supplied to passageway 142. Fluidinitially flows through passageway 142 into ports 140 and continues toflow until such time that a sufficient pressure develops withinpassageway 142 to open the valves 130 by means of applying pressure tosuch valves 78 through external portals 144 thereof. When such valves130 are open the pressure buildup within cylinder 134 outward to pistonhead 136 urges the piston head 136 inward from the extended positionthereof. Because the piston heads 136 are directly connected torespective cutting heads 78 by means of piston rods 138, such an inwardmovement of piston heads 136 causes the cutting heads extensions 78 toretract inwardly from the extended position thereof.

Hydraulic pressure fluid is selectively supplied to the internalpassageway of tube 128 or external passageway 142 through respectivegear casing extension portion 72 right hand and left hand respectively,passageways generally indicated at 146 and 148. As viewed in FIG. 2,passageway 146 is located within the left gear casing extension portion72 and passageway 148 is within the right extension portion 72.Passageways 146 and 148 extend radially inwardly from the rearward endsof extension portions 72 to a point intermediate the inner and outerdiameter of portions 72 whereat passageways 146 and 148 turnapproximately 90 and extend outwardly (i.e., away from the centerline ofmachine 10 parallel to the axis of shaft 70) to a point inwardlyadjacent the outer ends of extensions 72. From such a point passageways146 and 148 extend radially inwardly and open end at the inner peripheryof extension 72. Each passageway 146 and 148 communicate with an annulargrooves in the outer periphery of a respective drive shaft keeper 98.Each groove 160 is in communication with annular grooves 164 located atthe inner periphery of keepers by means of a plurality ofcircumferentially spaced passageways 162 which extend radially betweengrooves 160 and 164. Grooves 160 and 164 are in a staggered relationshipto one another such that one end of passageways 162 open ends at anouter portion of groove 160 and the other end thereof open ends at aninner end portion of groove 164.

Grooves 164 are in communication with grooves 166 located at the innerperiphery ofspacer sleeves 96 by means of a plurality ofcircumferentially spaced passageways 165. Passageways 165 open end atthe outer periphery of a spacer sleeve 96 in communication with a groove164 and extends radially inwardly therefrom to a groove 166.

With such a groove and passageway arrangement as hereinabove-describedhydraulic pressure fluid is supplied to tube 128 for extending rotarydrum cutting heads 80 in a manner hereinbefore described by flowingpressure fluid through passageway 146 into groove 160, throughpassageways 162 into groove 164, through passageway 165 into groove 166and through at least one tube 168 which extends radially inwardly ofshaft 70 and communicates between 166 and tube 128. Similarly, pressurefluid is supplied to passageway 142 to retract rotary drum cutting heads80 in a manner hereinbefore described by flowing pressure fluid throughpassageway 148 into groove 160, through passageways 163 into groove 164,through passagways 165 into groove 166 and through at least onepassageway 170 which extends radially inwardly of shaft 70 and has theradial outer end thereof communicating with groove 166 and the radialinner end thereof open ended in passageway 148.

Annular static seals such as rings 180 are suitably received in suitablegrooves between the outer periphery of drive shaft keepers 98 and theinner periphery of gear casing extension portions 72 and between theinner periphery of spacer sleeves 96 and the outer periphery of shaft70. Selfpressurizing expanding, type seal rings 182 are suitablyreceived in suitable grooves between the inner periphery of keepers 98and the outer periphery of spacer sleeves 96. Seal rings 180 and 182 arepositioned adjacent both sides of respective grooves 160, 166 and 168 toprevent pressure hydraulic fluid from flowing out of the sides of suchgrooves. It is to be noted that rings 182 must be of a self-pressurizingexpanding type because of the rotating movement of sleeves 96 withrespect to the stationary keepers 98.

It is to be noted that because the seal rings 180 and 182 are locatedoutwardly of roller bearings 94 the replacement of such seals isrelatively simple, for the bearings 94 need not be disturbed and thecasing extension portions 72 can remain in place during the removal ofworn seal rings 180 and 182 and the insertion of replacements. It isadditionally noted that by the use of grooves 160, 164 and 166 ofsubstantial axial dimension, a relative movement between adjacentpassageways of an amount substantially equal to the width of suchgrooves is possible without impairing the continuous flow of hydraulicpressure fluid to and away from passageways 146 and 148. Also thestaggering of grooves 160 and 164 is desirable so as keep the reductionof the cross-sectional area of keepers 98 at a minimum at any particularpoint.

Hydraulic fluid is drawn from a suitable fluid reservoir 149 by mans ofa pump 184. Hydraulic fluid passes through pump 184 and is furnishedunder pressure to a valve 186 which selectively channels the fluid toeither passageway 146 or 148. As is well known, fluid flowing throughone passageway of such a circuit displaces fluid from the cylinders 134through the other passageway, through the valve 186 and into thereservoir 149.

A preferred embodiment of this invention having been hereinbcforedescribed and herewith illustrated it is to be realized that variationsin the specific structure are envisioned and contemplated as furtherembodiment of the principles of this invention. It is thereforerespectfully requested that this invention be interpreted as broadly aspossible and limited only by the scope of the appended claims.

What is claimed is:

1. A mining machine cutting structure comprising: a support member; anelongated mining head member mounted at the forward end of said supportmember for powered rotation about a longitudinal axis of said headmember and having axially extensible and retractable end portion; saidmining head member including a longitudinally extending tubular headshaft transmitting power for said powered rotation, said support memberhaving extension portions for supporting said head shaft at axiallyspaced portions thereof; and elongated member coaxially received withinsaid head shaft and inwardly spaced from at least a portion of the innersurface thereof to form an elongated chamber in conjunction therewith,said elongated member having an axial bore extending therein; each ofsaid extension portions having a passageway therein, said passagewayscommunicating at one end thereof with said axial bore and said chamber,respectively, and said passageways, at the other ends thereof, adaptedto be selectively connected to individual ones of a pressure fluidsource and a fluid reservoir; and fluid operable extensible meansconnected to said reciprocable end portions and operatively connected tosaid chamber and said bore for the selective extension and retraction ofsaid reciprocable end portions.

2. A mining machine cutting structure as specified in claim 1 whereinsaid fluid operably extensible means comprise a pair of axially spacedextensible hydraulic cylinder assemblies secured within each end of saidhead shaft, each of said cylinder assemblies having respective pistons,rods, rod ends and head ends.

3. A mining machine cutting structure as specified in claim 2 whereineach of said head ends have a pilot-operated check valve mounted thereoncommunicating through said check valve with said axial bore, each ofsaid rod ends communicating with said chamber, and control portal meanscommunicating between said check valve and said chamber for thereceiving a flow of unlocking pressure fluid into said check valve.

4. A mining machine cutting structure as specifiedin claim 1additionally including bearing means disposed intermediate said supportmember extension portions and said head shaft at said axially spacedportions.

5. A mining machine cutting structure as specified in claim 4 includingsealing means disposed intermediate said support member extensionportions and said head shaft axially outwardly of each of said bearingmeans and each of said passageways extending through respective ones ofsaid sealing means.

6. A mining machine cutting structure as specified in claim 1 whereinsaid bore supplies pressure fluid for the extension of said end portionsand said chamber provides pressure fluid for the retraction of said endportions.

7. In a mining machine of the type having a forwardly extending supportmember with an elongated mining head member transversely mounted at theforward end of said support member for powered rotation about thecentral longitudinal axis of said head member and in which said supportmember includes a casing rotatably supporting an elongated head shafttransmitting power for said powered rotation mounted within outwardlyextending casing extension portions encompassing axially spaced portionsof said head shaft the improvement wherein; said head shaft has an axialthrough bore; an elongated member within said shaft inwardly spaced fromat least a portion of the inner surface of said bore forming a pair ofaxial passageways within said bore, each of said casing extensionportions has a passageway therein communicating selectively at one endwith an external source of pressure fluid and a fluid-receiving tankalternatively, and the other ends of said casing passagewayscommunicating with fluid tight means in turn communicating withindividual ones of said pair of axial passageways respectively.

8. In a mining machine as specified in claim 7 the further improvementwherein; bearing means are mounted within said casing extension portionsinwardly adjacent the outer ends of said casing portions to support saidshaft and wherein said fluidtight means comprises sealing meansencompassing said shaft located axially outwardly of each of saidbearing means and mounted at least partially within the outer ends ofsaid casing portions to provide liquid-tight relationship between saidshaft and said casing portions.

9.'In a mining machine as specified in claim 8 the further improvementwherein each of said sealing means is interposed between a spacer sleevesecured in fluidtight relationship on the outer surface of said headshaft and an annular keeper member secured within the outer end of eachof said casing extension portions in fluidtight relationship therewithand said keeper member and said sleeve had intercommunicating passagewaymeans therein.

10. in a mining machine as specified in claim 9 the further improvementwherein said passageway means in said keeper member comprises anexternal peripheral groove and an internal peripheral groove in saidkeeper member communicating with each other through at least one radialopening open ended in both grooves and said passageway means in saidspacer sleeve comprise a groove in the internal peripheral surfacethereof communicating with the external surface of said sleeve throughat leas one radial opening in said sleeve.

11. In a mining machine as specified in claim 9 the further improvementwherein said spacer sleeves rotate with said shaft and said keepers areheld stationary by said casing extension.

12. In a mining machine as specified in claim 7 the further improvementwherein said bore has an extensible hydraulic cylinder assembly securedwithing each end thereof, said cylinder assemblies having respectivepistons, rods, rod ends and head ends, each head end having a pilotoperated check valve mounted thereon and communicating through saidvalve with one of said axial passageways, each said rod endcommunicating with the other of said axial passageways, and each saidpilot operated check valve communicating with said other passagewaythrough a control portal for receiving unlocking pressure fluid.

13. In a mining machine as specified in claim 12 the further improvementwherein a pair of cutter-carrying drums is mounted on axially spacedportions of said head shaft and said drums have axially slidable drumextension portions mounted therein, each said drum extension portionbeing secured to a respective one of said rod ends to be selectivelymoved axially thereby, said axial movement being effected by saidselective connecting of said casing extension passageways with saidsource of fiuid pressure and said tank, respectively.

1. A mining machine cutting structure comprising: a support member; an elongated mining head member mounted at the forward end of said support member for powered rotation about a longitudinal axis of said head member and having axially extensible and retractable end portion; said mining head member including a longitudinally extending tubular head shaft transmitting power for said powered rotation, said support member having extension portions for supporting said head shaft at axially spaced portions thereof; and elongated member coaxially received within said head shaft and inwardly spaced from at least a portion of the inner surface thereof to form an elongated chamber in conjunction therewith, said elongated member having an axial bore extending therein; each of said extension portions having a passageway therein, said passageways communicating at one end thereof with said axial bore and said chamber, respectively, and said passageways, at the other ends thereof, adapted to be selectively connected to individual ones of a pressure fluid source and a fluid reservoir; and fluid operable extensible means connected to said reciprocable end portions and operatively connected to said chamber and said bore for the selective extension and retraction of said reciprocable end portions.
 2. A mining machine cutting structure as specified in claim 1 wherein said fluid operably extensible means comprise a pair of axially spaced extensible hydraulic cylinder assemblies secured within each end of said head shaft, each of said cylinder assemblies having respective pistons, rods, rod ends and head ends.
 3. A mining machine cutting structure as specified in claim 2 wherein each of said head ends have a pilot-operated check valve mounted thereon communicating through said check valve with said axial bore, each of said rod ends communicating with said chamber, and control portal means communicating between said check valve and said chamber for the receiving a flow of unlocking pressure fluid into said check valve.
 4. A mining machine cutting structure as specified in claim 1 additionally including bearing means disposed intermediate said support member extension portions and said head shaft at said axially spaced portions.
 5. A mining machine cutting structure as specified in claim 4 including sealing means disposed intermediate said support member extension portions and said head shaft axially outwardly of each of said bearing means and each of said passageways extending through respective ones of said sealing means.
 6. A mining machine cutting structure as specified in claim 1 wherein said bore supplies pressure fluid for the extension of said end portions and said chamber provides pressure fluid for the retraction of said end portions.
 7. In a mining machine of the type having a forwardly extending support member with an elongated mining head member transversely mounted at the forward end of said support member for powered rotation about the central longitudinal axis of said head member and in which said support member includes a casing rotatably supporting an elongated hEad shaft transmitting power for said powered rotation mounted within outwardly extending casing extension portions encompassing axially spaced portions of said head shaft, the improvement wherein; said head shaft has an axial through bore; an elongated member within said shaft inwardly spaced from at least a portion of the inner surface of said bore forming a pair of axial passageways within said bore, each of said casing extension portions has a passageway therein communicating selectively at one end with an external source of pressure fluid and a fluid-receiving tank alternatively, and the other ends of said casing passageways communicating with fluid tight means in turn communicating with individual ones of said pair of axial passageways respectively.
 8. In a mining machine as specified in claim 7 the further improvement wherein; bearing means are mounted within said casing extension portions inwardly adjacent the outer ends of said casing portions to support said shaft and wherein said fluidtight means comprises sealing means encompassing said shaft located axially outwardly of each of said bearing means and mounted at least partially within the outer ends of said casing portions to provide liquid-tight relationship between said shaft and said casing portions.
 9. In a mining machine as specified in claim 8 the further improvement wherein each of said sealing means is interposed between a spacer sleeve secured in fluidtight relationship on the outer surface of said head shaft and an annular keeper member secured within the outer end of each of said casing extension portions in fluidtight relationship therewith and said keeper member and said sleeve had intercommunicating passageway means therein.
 10. In a mining machine as specified in claim 9 the further improvement wherein said passageway means in said keeper member comprises an external peripheral groove and an internal peripheral groove in said keeper member communicating with each other through at least one radial opening open ended in both grooves and said passageway means in said spacer sleeve comprise a groove in the internal peripheral surface thereof communicating with the external surface of said sleeve through at leas one radial opening in said sleeve.
 11. In a mining machine as specified in claim 9 the further improvement wherein said spacer sleeves rotate with said shaft and said keepers are held stationary by said casing extension.
 12. In a mining machine as specified in claim 7 the further improvement wherein said bore has an extensible hydraulic cylinder assembly secured withing each end thereof, said cylinder assemblies having respective pistons, rods, rod ends and head ends, each head end having a pilot operated check valve mounted thereon and communicating through said valve with one of said axial passageways, each said rod end communicating with the other of said axial passageways, and each said pilot operated check valve communicating with said other passageway through a control portal for receiving unlocking pressure fluid.
 13. In a mining machine as specified in claim 12 the further improvement wherein a pair of cutter-carrying drums is mounted on axially spaced portions of said head shaft and said drums have axially slidable drum extension portions mounted therein, each said drum extension portion being secured to a respective one of said rod ends to be selectively moved axially thereby, said axial movement being effected by said selective connecting of said casing extension passageways with said source of fluid pressure and said tank, respectively. 